| sec : U Re: Proper pointer cleanup question [message #34647] |
Tue, 08 April 2003 18:34  |
Andrew Cool
Messages: 219
Registered: January 1996
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Senior Member |
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Paul van Delst wrote:
>
>
> <snip>
>
>> Another option is:
>>
>> heap_free,a
>>
>
> Wha..? Is that another one of those undocumented IDL routines? It works on my current
> version, but bugger me if I can find it documented anywhere.
>
> paulv
>
> --
Paul,
Ben Tucker's CoolHelp says :-
HEAP_FREE
The HEAP_FREE procedure recursively frees
all heap variables (pointers or objects)
referenced by its input argument. This
routine examines the input variable, including
all array elements and structure fields.
When a valid pointer or object reference is
encountered, that heap variable is marked
for removal, and then is recursively
examined for additional heap variables to be
freed. In this way, all heap variables that
are referenced directly or indirectly by the
input argument are located. Once all such
heap variables are identified, HEAP_FREE
releases them in a final pass. Pointers are
released as if the PTR_FREE procedure was
called. Objects are released as with a call
to OBJ_DESTROY.
As with the related HEAP_GC procedure,
there are some disadvantages to using
HEAP_FREE such as:
* When freeing object heap
variables, HEAP_FREE calls OBJ_DESTROY
without supplying any plain or keyword
arguments. Depending on the objects
being released, this may not be sufficient.
In such cases, the caller must call
OBJ_DESTROY explicitly with the
proper arguments rather than using
HEAP_FREE.
* HEAP_FREE releases the referenced
heap variables in an unspecified order
which depends on the current state of the
internal data structure used by IDL to
hold them. This can be confusing for
object destructor methods that expect all
of their contained data to be present.
If your application requires a specific
order for the release of its heap variables,
you must explicitly free them in the
correct order. HEAP_FREE cannot be used in such cases.
* The algorithm used by HEAP_FREE to
release variables requires examination
of every existing heap variable (that
is, it is an O(n) algorithm). This may be
slow if an IDL session has
thousands of current heap variables.
For these reasons, Research Systems recommends
that applications keep careful track
of their heap variable usage, and explicitly
free them at the proper time (for example,
using the object destructor method) rather
than resorting to simple-looking but
potentially expensive expedients
such as HEAP_FREE or HEAP_GC.
HEAP_FREE is recommended when:
* The data structures involved are
highly complex, nested, or variable, and
writing cleanup code is difficult and error prone.
* The data structures are opaque,
and the code cleaning up does not have
knowledge of the structure.
Syntax
HEAP_FREE, Var [, /OBJ] [, /PTR] [, /VERBOSE]
Arguments
Var
The variable whose data is used as the
starting point for heap variables to be freed.
Keywords
OBJ
Set this keyword to free object heap variables only.
PTR
Set this keyword to free pointer heap variables only.
Note
Setting both the PTR and OBJ keywords
is the same as setting neither.
VERBOSE
If this keyword is set, HEAP_FREE writes
a one line description of each heap
variable, in the format used by the HELP
procedure, as the variable is released. This
is a debugging aid that can be used by
program developers to check for heap variable
leaks that need to be located and eliminated.
Example
; Create a structure variable.
mySubStructure = {pointer:PTR_NEW(INDGEN(100)), $
obj:OBJ_NEW('Idl_Container')}
myStructure ={substruct:mySubStructure, $
ptrs:[PTR_NEW(INDGEN(10)), PTR_NEW(INDGEN(11))]}
;Look at the heap.
HELP, /HEAP_VARIABLES
; Now free the heap variables contained in myStructure.
HEAP_FREE, myStructure, /VERBOSE
HELP, /HEAP_VARIABLES
See Also
HEAP_GC
Andrew.
------------------------------------------------------------ -----------------
Andrew D. Cool
Electromagnetics & Propagation Group
Intelligence, Surveillance & Reconnaissance Division
Defence Science & Technology Organisation
PO Box 1500, Edinburgh
South Australia 5111
Phone : 061 8 8259 5740 Fax : 061 8 8259 6673
Email : andrew.cool@no-spam.dsto.defence.gov.au
------------------------------------------------------------ -----------------
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